Piano tone-synthesizing system for electronic musical instruments

ABSTRACT

A piano tone-synthesizing system for an electronic musical instrument comprising tone generators and a keyboard provided with a plurality of keys. Operation of each key on the keyboard causes tone signals of 4&#39;&#39;, 8&#39;&#39; and 16&#39;&#39; to be derived from the tone generators by a keyer. The tone signals of 4&#39;&#39;, 8&#39;&#39; and 16&#39;&#39; are supplied with the color of flute tones by flute tone coloring filters. The tone signals of 4&#39;&#39; and 8&#39;&#39; are further furnished with the colors of brass and string tones by a brass tone coloring filter and a string tone coloring filter. The tone signals bearing the various tone colors are mixed to provide a piano tone.

United States Patent 11 1 1111 3,836,693 Ichikawa Sept. 17, 1974 [54] PIANO TONE-SYNTHESIZING SYSTEM 3,591,699 7/ 1971 Cutler 84/].11 FOR ELECTRONIC MUSICAL 3,624,265 11/1971 Yamada... 84/l.19 3,723,633 3/1973 Adachi 84/l.01 INSTRUMENTS 3,739,071 6/1973 Niinomi... 84/1.l9 [75] inventor: Kiyoshi Ichikawa, l-lamakita, Japan 3,749,807 7/1973 Adachi 8 1 X 3,757,023 9 1973 P t 841 ll 73 Assignee: Nippon Gakki Seizo Kabushiki 6 I shlzuoka'ken Japan Primary Examiner-Richard B. Wilkinson [22] Filed: June 28, 1973 Assistant Examiner-Stanley .l. Witkowski [2]] App]. No: 374,309 Attorney, Agent, or Fzrm-Flynn & Frishauf 57 ABSTRACT Foreign Application Priority Data J 30 1972 J 47 65488 A p1an0 tone-synthes1z1ng system for an electronic une apan musical instrument comprising tone generators and a keyboard provided with a plurality of keys. Operation [52] U.S. Cl 84/119, 84/1.2l48/l1)/Il(.3239, of each key on the keyboard causes tone signals [51] Int Cl Glob 5/02 8' and 16 to be derived from the tone generators by a [58] i 1 19 I 24 keyer. The tone signals of 4, 8 and 16 are supplied 1 a c b with the color of flute tones by flute tone coloring til- 2 ters. The tone signals of 4 and 8 are further furnished with the colors of brass and string tones by a [56] References Clted brass tone coloring filter and a string tone coloring fil- UNITED STATES PATENTS ter. The tone signals bearing the various tone colors 2,142,580 1/1939 Williams 84/121 are mixed to provide a piano tone. 2,580,217 12/1951 Colombani 84 122 3,505,461 4/1970 Omura et al 84/1.0l 18 ClalmS, 9 Drawing gures l l l? re *4 4 r 4' FLUTE 22k 1 16' MIXER FILTER W I v 1 e ,18 {6 5: J7 1 8 e FLUTEAWW m 1 El MIXER FILTER 26 30 O 0: 20 1 I" 1 LL] 1 1 1 16 16 mm look l 5 MIXER L FILTER OUTPUT l 1 H k I 4 BRASS 1 MIXER L FILTER i H 124 1 s STRING k 23-MIXER L FILTER 1 PAIENTEDSEFI mm v 3.836.693

414 FIG. 1.

6 4 FLUTE 22k FTLTER Fl T i6 9 MIXER L FU'ER 7 OUTPUT 4 U H 120k 2 8 150k ILTER a 2 MIXER LEVEL LEVEL- MIXER OUTPUT MIXER OUTPUT LOW H'IGH F IG. 2D

MIXER OUTPUT LEVEL LOW 1 HIGH OUTPUT PIANO TONE-SYNTHESIZING SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS BACKGROUND OF THE INVENTION This invention relates to a piano tone-synthesizing system for electronic musical instruments.

In an electronic musical instrument fundamental tone signals produced by the tone generators are combined in various combinations to provide musical tone signals bearings various tone colors, using filters having different frequency characteristics. To elevate the effect of performance, selection is further made, for example, of couplers, filters and envelopes associated with musical tones being played.

To produce musical tones resembling piano tones by the prior art electronic musical instrument, tone signals generated by the tone generators with rectangular waves are delivered through a keyer upon key operation while being accompanied with the so-called percussive envelope attenuating immediately after the rise. The tone signals are later passed through a filter to be supplied with, for example, the color of flute tones. This process provides musical tones like percussive tones, one of the characteristics of piano tones. Musical tones thus obtained indeed present such volume change or envelope change as simulates piano tones. However, those musical tones only bear a simple tone color, falling short of actual piano tones.

SUMMARY OF THE INVENTION It is accordingly the object of this invention to provide a piano tone-synthesizing system enabling musical tones bearing tone colors more truthful to the characteristics of piano tones than possible with prior art electronic musical instruments.

The piano tone-synthesizing system of this invention essentially comprises a keyboard provided with a plurality of keys; tone generators; a keyer for deriving 4, 8' and 16 tone signals from the tone generators in response to operation of each key on the keyboard; a first tone coloring filter for imparting the color of flute tones to the 4 tone signal; a second tone coloring filter for supplying the color of flute tones to the 8' tone signal; a third tone coloring filter for giving the 16 tone signal the color of flute tones; a fourth tone coloring filter for furnishing the 4' and 8' tone signals with the color of brass tones; a fifth tone coloring filter for supplying the 4 and 8' tone signals with the color of string tones; and means for mixing output signals from the first to fifth tone coloring filters.

According to the piano tone-synthesizing system of this invention, the 8' flute tone signal defines the pitch of musical tones, and the 16' flute tone signal emphasizes the low compass of musical tones, thereby causing the musical tones to display forcefulness and massiveness. The 4' tone signal renders particularly the high compass prominent, providing the effect of string tones. Addition of the color of string tones to the musical tones enables the listener to feel such vibrations as are derived from piano strings. Further, the color of brass tones supplied to the musical tones renders particularly the high compass thereof very brilliant.

The system of this invention enables musical tones including the percussive tones, strong tones and the tones derived from the sound boards which characterize piano tones to be produced over a range from the low to the high compass, namely, provides forceful percussive tones in the low compass and resounding percussive tones in the high compass always in a brilliant state.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a piano tone-synthesizing system according to an embodiment of this invention;

FIGS. 2A to 2C are mixing characteristics of mixers of FIG. 1 used in combining tone signals of 4', 8 and 16' respectively;

FIG. 2D is a circuit diagram of a mixer for the tone signals;

FIG. 3A is a circuit diagram of one mixer of FIG. 1 for the tone signals of 4 and 8;

FIG. 3B shows characteristics of the mixer of FIG. 3A;

FIG. 4 is a block diagram of a piano tone-synthesizing system according to another embodiment of the invention; and

FIG. 5 as a fractional circuit diagram of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, numeral 11 denotes the known tone generators for producing tone signals. Output signals from the tone generators 11 are conducted to the known keyer 12, which, upon key depression, selectively draws out from the tone generators tone signals having a pitch corresponding to a depressed key and including 4', 8 and 16' tone signals mutually bearing a coupler relationship. From the keyer 12 are jointly delivered tone signals falling within the predetermined compass or a half octave compass. Supposing that the keyboard 13 has five octave compasses, then the keyer 12 is provided with 10 output terminals for the 4' tone signal, and also l0 output terminal for the 8' and 16' tone signals respectively. The fundamental pitch of the note of a depressed key is determined by the 8 tone signal. The 16' tone signal has a frequency one octave lower than that of the 8 tone signal and the 4 tone signal has a frequency one octave higher than that of the 8 tone signal. The keyer 12 may be so designed as to produce tone signals bearing such a percussive envelope as indicated by numeral 14.

A plurality of 4 tone signals delivered from the keyer 12 are properly combined by a mixer 15. A mixed output signal is supplied to a tone coloring filter 16 to be furnished with the color of flute tones. Similarly, a group of 8' tone signals and that of 16 are combined by mixers 17 and 19 respectively, and than conducted to tone coloring filters 18 and 20 respectively so as to be given the color of flute tones.

A group of4i' tone signals and that of 8' tone signals are further combined by mixers 21 and 23 respectively. These mixers 21 and 23 are each provided with a first output terminal H f0 mainly deriving tone signals of high frequency and a second output terminal L for mainly deriving tone signals of low frequency. The first and second output terminals H and L of the mixers 21 and 23 are connected to a tone coloring filter 22 for imparting the color of brass tones to the 4' and 8 tone signals. Further the second output terminals L of the mixers 21 and 23 are connected to a tone coloring filter 24 for supplying the color of string tones to the 4' and 8' tone signals. Musical tone signals from the tone color filters 16, 18, 20, 22 and 24 are properly combined by resisters 25 to 29 and then conducted to an amplifier 30.

The mixer 15 for the 4' tone signals is preferred to have such a frequency characteristic as cause the levels of mixed tone signals progressively to decrease, as shown in FIG. 2A, as the frequencies thereof fall. The mixer 17 for the 8' tone signals defining the fundamental pitch of musical tones is designed to have a flat frequency characteristic indicated in FIG. 28 whereby tone signals having different frequencies are mixed with an equal level. On the other hand, the mixer 19 for the 16 tone signals is desired to display, as shown in FIG. 2C, the opposite frequency characteristic to that of the mixer 15 for the 4" tone signals.

The mixers 21 and 23 are arranged, as illustrated, for example, in FIG. 3A. These mixers 21 and 23 each have ten input terminals to match the keyboard 13 having five octave compasses. Resistors R of equal resistivity are connected at one end to the input terminals. The resistors R are connected at the other end successively to resistors R1 of equal resistivity. The input terminals are supplied with tone signals whose frequencies progressively increase from the first to the tenth input terminal. The first output terminal H is connected to that terminal a serial circuit consisting of resistors R1 which is located at the side of the tenth input terminal supplied with a tone signal of highest frequency. The second output terminal L is connected to that terminal of the serial circuit consisting of resistors R1 which is located at the side of the first input terminal, supplied with a tone signal of lowest frequency.

Where, therefore, the input terminals are supplied with tone signals having an equal level, then there are delivered, as shown in FIG. 38, from the first output terminal H a plurality of tone signals whose levels progressively fall as their frequencies decrease, and from the second output terminal L a plurality of tone signals whose levels are successively reduced as their frequencies increase.

Musical tone signals delivered from the tone coloring filters 16, 18, 20, 22 and 24 may be combined by the resistors 25 to 29 in the following proportions:

4' tone signals supplied with the color of flute tones l 8' tone signals supplied with I the color of flute tones I I6 tone signals supplied with The mixers 15 and 19 of FIG. 1 may be arranged as shown in FIG. 3A. In this case, the mixer 15 need not be provided with the second output terminal L, nor the mixer 19 requires the first output terminal H. The mixer 17 may have the arrangement of FIG. 3A. In this case, both first and second output terminals H and L are connected to the tone color filter 18. Or the mixers 15, 17 and 19 may consist of mixers including as shown in FIG. 2D, ordinary mixing resistors r1 to r10. In this case, the mixers l and 19 include mixing resistors r1 to r having sequentially different values and the mixer 17 include mixing resistors rll to r10 having an equal value. The mixers l5 and 19 may further consist of active elements or transistors having different amplification factors. Either of the mixers 15 and 21 for the 4' tone signals may be concurrently used as a substitute for the other. Similarly either of the mixers 17 and 23 for the 8'. tone signals may be concurrently used as a substitute for the other. Further, either of the mixer 21 for the 4 tone signals and the mixer 23 for the 8' tone signals may be used in mixing the 4 and 8' tone signals at the same time. Supply of the 4' and 8 tone signals to the brass tone coloring filter 22 may be effected by two mixers each having the same flat frequency characteristics as those of the mixer 17. In this case, supply of 4 and 8' tone signals to the string tone coloring filter 24 is carried out using a mixer having the same arrangement as shown in FIG. 3A but only provided with the second output terminal L or a mixer including the mixing resistors r1 and r10 of FIG. 2D having different values.

In the embodiment of FIG. 1, there were used the mixers 15, and 19 having the frequency characteristics shown in FIGS. 2A and 2C as means for varying the levels of 4 and 16' tone signals supplied to the flute tone coloring filter l6 and 20 according to their frequencies. However, these mixers are not always necessary. Namely, the same effect can be attained by supplying, as shown in FIG. 4, the 4' and 16 tone signals directly to the flute tone coloring filters l6 and 20 and providing a high pass filter 31 and low pass filter 32 on the output side of the flute tone coloring filters 16 and 20. The high pass filter 31 delivers tone signals having such frequency characteristics as shown in FIG. 2A, and the low pass filter produces tone signals having such frequency characteristics as illustrated in FIG. 2B. The high and low pass filters 31 and 32 may be disposed on the input side of the flute tone coloring filters 16 and 20.

FIG. 5 illustrates the circuit arrangement of the high and low pass filters 31 and 32, brass tone coloring filter 22 and string tone coloring filter 24. The high pass filter 31 is desired to have a cutoff frequency of 600 to 700 Hz (-6 db/oct) and the low pass filter a cutoff frequency of to 200 Hz (-6 db/oct).

What is claimed is: 1. A method for synthesizing piano tones using an electronic musical instrument including a keyboard means having a plurality of keys for initiating tone generation and a plurality of tone generators comprising the steps of:

coupling out tone signals of 4', 8' and 16' from said tone generators in response to operation of at least one key on said keyboard;

imparting the color of flute tones to the 4' tone signal having a predetermined amplitude and forming a first musical tone signal;

imparting the color of flute tones to the 8' tone signal having a predetermined amplitude and forming a second musical tone signal;

imparting the color of flute tones to the 16 tone signal having a prescribed amplitude and forming a third musical tone signal; imparting the color of brass tones to the 4' and 8' tone signals, each having a predetermined amplitude, and forming a fourth musical tone signal; imparting the color of string tones to the 4' and 8' tone signals, each having a predetermined amplitude, and forming a fifth musical tone signal; and

combining said first to fifth musical tone signals in a predetermined ratio for producing a synthesized tone signal.

2. A system according to claim 1 comprising combining the respective musical tone signals in a ratio of substantially lzlztllzfilfiflld.

3. A system according to claim 1 comprising deriving said 4', 8 and 16' tone signals from said tone generators with respective percussive envelopes.

4. A piano tone synthesizing system for electronic musical instruments comprising:

keyboard means having a plurality of keys for initiating tone generation;

a plurality of tone generators;

keyer means for coupling out tone tone signals of 4', 8 and 116' from said tone generators in response to operation of each key of said keyboard means;

a first tone coloring filter means coupled to said keyer means for supplying said 4' tone signal with the color of flute tones;

a second tone coloring filter means coupled to said keyer means for supplying said 8' tone signal with the color of flute tones;

a third tone coloring filter means coupled to said keyer means for suppying the color of flute tones to said 16; tone signal;

a fourth tone coloring filter means coupled to said keyer means for supplying the 4' and 8 tone signals with the color of brass tones;

a fifth tone coloring filter means coupled to said keyer means for supplying said 4' and 8' tone signals with the color of string tones; and

means for combining output signals from said first to fifth tone coloring filters to generate a synthesized tone signal.

5. A system according to claim 4 further comprising amplitude varying means coupled to said first tone coloring filter means for progressively reducing the amplitudes of a plurality of 3 tone signals delivered from said keyer means in response to operation ofa plurality of keys on said keyboard means as their frequencies decrease.

6. A system according to claim 5 wherein said amplitude varying means comprises a high pass filter.

7. A system according to claim 5 wherein said amplitude varying means comprises a mixer coupled between said keyer and said first tone coloring filter.

8. A system according to claim 7 wherein said mixer includes a plurality of input terminals; one output terminal coupled to the input of said first tone coloring filter; a plurality of first resistors of equal resistance connected at one end to the plural input terminals respectively; and a plurality of second serially connected resistors of equal resistance successively interconnecting the opposite ends of said first resistors with at least one second resistor coupled between successive opposite ends of said first resistors, one end of said serial connection of said second resistors being connected to said output terminal, and said input terminals being supplied with the 4 tone signals whose frequencies progressively decrease from the input terminal coupled to the first resistor which is connected at its said other end to the output end of said serial connection of said second resistors toward the input terminals successively coupled at points along said serial connection of said second resistors.

9. A system according to claim 8 wherein said input terminals of said mixer are each supplied with a plurality of a tone signals falling within a predetermined compass collectively.

10. A system according to claim 4 further comprising amplitude varying means coupled to said third tone coloring filter means for progressively reducing the amplitudes of a plurality of 16' tone signals delivered from said keyer means in response to operation of a plurality of keys on said keyboard means as their frequencies increase.

lll. A system according to claim 10 wherein said amplitude varying means is a low pass filter.

12. A system according to claim 10 wherein said amplitude varying means is a mixer connected between said keyer means and said third tone coloring filter.

13. A system according to claim 12 wherein said mixer includes a plurality of input terminals, one output terminal coupled to the input of said third tone coloring filter means, a plurality of first resistors of equal resistance connected at one end of said plural input terminals respectively; and a plurality of second serially connected resistors of equal resistance successively interconnecting the opposite ends of said first resistors with at least one second resistor coupled between successive opposite ends of said first resistors, one end of said serial connection of said second resistors being connected to said output terminal, and said input terminals being supplied with 16 tone signals whose frequencies progressively increase from the input terminal coupled to the first resistor which is connected at its said other end to the output end of said serial connection of said second resistors toward the input terminals successively coupled at points along said serial connection of said second resistors.

14. A system according to claim 10 wherein said input terminals of said mixer are each supplied with a plurality of 16 tone signals falling within a predetermined compass collectively.

15. A system according to claim 4 further including amplitude varying means coupled to said fifth tone coloring filter means for progressively reducing the amplitudes of a plurality of 4' tone signals and those of a plurality of 8' tone signals delivered from said keyer in response to operation of a plurality of keys on said keyboard means as their frequencies increase.

16. A system according to claim 4 further comprising a first amplitude varying means connected between said keyer means and said fourth tone coloring filter means and a second amplitude varying means connected between said keyer means and said fifth tone coloring filter means; said first and second amplitude varying means each having a plurality of input terminals, a first and a second output terminal, a plurality of first resistors successively connected at one end to the plural input terminals respectively, and a plurality of second serially connected resistors of equal resistivity successively interconnecting the opposite ends of said plural first resistors with at least one second resistor coupled between successive opposite ends of said first resistors; said first and second output terminals being connected to the end terminals of the serial circuit comprised of said serially connected second resistors; said plural input terminals of each of said first and second amplitude varying means being so connected to said keyer means as to receive a group of 4' tone signals and that of 8 tone signals respectively whose frequencies progressively decrease from the input terminal which is coupled to the first resistor which is connected at its said other end to said first output terminal toward the input terminal which is coupled to the first resistor which is connected at its said other end to said second output terminal; said first and second output terminals of said first and second amplitude varying means being connected to said fourth tone coloring filter; and said second output terminal of each of said first and second amplitude varying means being connected to said fifth tone coloring filter.

17. A piano tone-synthesizing system for electronic musical instruments comprising:

keyboard means having a plurality of keys for initiating tone generation; a plurality of tone generators; keyer means for coupling out tone signals of 4, 8' and 16' from said tone generators in response to operation of at least one key of said keyboard means; means coupled to the output of said keyer means for forming a first musical tone signal, said means including a tone coloring filter means for supplying the 4' tone signals with the color of flute tone and means coupled to said tone coloring filter means for varying the levels of the 4' tone signals as a function of their frequencies over a given range of frequencies; means coupled to the output of said keyer means for forming a second musical tone signal, said means including a tone coloring filter means for supplying the 8 tone signals with the color of flute tones;

means coupled to the output of said keyer means for forming a third musical tone signal, said means incluidng a tone coloring filter means for imparting the color of flute tones to the 16' tone signals and means coupled to said tone coloring filter for varying the levels of the 16 tone signals as a function of their frequencies over a given range of frequencies;

means coupled to the output of said keyer means for forming a fourth musical tone signal, said means including a tone coloring filter means for supplying the 4 and 8 tone signals with the color of brass tones;

means coupled to the output of said keyer means for forming a fifth musical tone signal, said means including a tone coloring filter means for supplying the 4 and 8' tone signals with the color of string tones and means coupled to said tone coloring filter means for varying the levels of the 4' 8 tone signals as a function of their frequencies over a given range of frequencies; and

means for combining said first to fifth musical tone signals in a predetermined ratio to generate a synthesized tone signal.

18. A system according to claim 17 wherein said predetermined ratio in which the respective musical tone signals are combined in substantially 1:1:0.2:0.16:0.l4. 

1. A method for synthesizing piano tones using an electronic musical instrument including a keyboard means having a plurality of keys for initiating tone generation and a plurality of tone generators comprising the steps of: coupling out tone signals of 4'', 8'' and 16'' from said tone generators in response to operation of at least one key on said keyboard; imparting the color of flute tones to the 4'' tone signal having a predetermined amplitude and forming a first musical tone signal; imparting the color of flute tones to the 8'' tone signal having a predetermined amplitude and forming a second musical tone signal; imparting the color of flute tones to the 16'' tone signal having a prescribed amplitude and forming a third musical tone signal; imparting the color of brass tones to the 4'' and 8'' tone signals, each having a predetermined amplitude, and forming a fourth musical tone signal; imparting the color of string tones to the 4'' and 8'' tone signals, each having a predetermined amplitude, and forming a fifth musical tone signal; and combining said first to fifth musical tone signals in a predetermined ratio for producing a synthesized tone signal.
 2. A system according to claim 1 comprising combining the respective musical tone signals in a ratio of substantially 1: 1:0.2:0.16:0.14.
 3. A system according to claim 1 comprising deriving said 4'', 8'' and 16'' tone signals from said tone generators with respective percussive envelopes.
 4. A piano tone synthesizing system for electronic musical instruments comprising: keyboard means having a plurality of keys for initiating tone generation; a plurality of tone generators; keyer means for coupling out tone tone signals of 4'', 8'' and 16'' from said tone generators in response to operation of each key of said keyboard means; a first tone coloring filter means coupled to said keyer means for supplying said 4'' tone signal with the color of flute tones; a second tone Coloring filter means coupled to said keyer means for supplying said 8'' tone signal with the color of flute tones; a third tone coloring filter means coupled to said keyer means for suppying the color of flute tones to said 16; tone signal; a fourth tone coloring filter means coupled to said keyer means for supplying the 4'' and 8'' tone signals with the color of brass tones; a fifth tone coloring filter means coupled to said keyer means for supplying said 4'' and 8'' tone signals with the color of string tones; and means for combining output signals from said first to fifth tone coloring filters to generate a synthesized tone signal.
 5. A system according to claim 4 further comprising amplitude varying means coupled to said first tone coloring filter means for progressively reducing the amplitudes of a plurality of 4'' tone signals delivered from said keyer means in response to operation of a plurality of keys on said keyboard means as their frequencies decrease.
 6. A system according to claim 5 wherein said amplitude varying means comprises a high pass filter.
 7. A system according to claim 5 wherein said amplitude varying means comprises a mixer coupled between said keyer and said first tone coloring filter.
 8. A system according to claim 7 wherein said mixer includes a plurality of input terminals; one output terminal coupled to the input of said first tone coloring filter; a plurality of first resistors of equal resistance connected at one end to the plural input terminals respectively; and a plurality of second serially connected resistors of equal resistance successively interconnecting the opposite ends of said first resistors with at least one second resistor coupled between successive opposite ends of said first resistors, one end of said serial connection of said second resistors being connected to said output terminal, and said input terminals being supplied with the 4'' tone signals whose frequencies progressively decrease from the input terminal coupled to the first resistor which is connected at its said other end to the output end of said serial connection of said second resistors toward the input terminals successively coupled at points along said serial connection of said second resistors.
 9. A system according to claim 8 wherein said input terminals of said mixer are each supplied with a plurality of 4'' tone signals falling within a predetermined compass collectively.
 10. A system according to claim 4 further comprising amplitude varying means coupled to said third tone coloring filter means for progressively reducing the amplitudes of a plurality of 16'' tone signals delivered from said keyer means in response to operation of a plurality of keys on said keyboard means as their frequencies increase.
 11. A system according to claim 10 wherein said amplitude varying means is a low pass filter.
 12. A system according to claim 10 wherein said amplitude varying means is a mixer connected between said keyer means and said third tone coloring filter.
 13. A system according to claim 12 wherein said mixer includes a plurality of input terminals, one output terminal coupled to the input of said third tone coloring filter means, a plurality of first resistors of equal resistance connected at one end of said plural input terminals respectively; and a plurality of second serially connected resistors of equal resistance successively interconnecting the opposite ends of said first resistors with at least one second resistor coupled between successive opposite ends of said first resistors, one end of said serial connection of said second resistors being connected to said output terminal, and said input terminals being supplied with 16'' tone signals whose frequencies progressively increase from the input terminal coupled to the first resistor which is connected at its said other end to the output end of said serial connection of said second resistors toward the input terMinals successively coupled at points along said serial connection of said second resistors.
 14. A system according to claim 10 wherein said input terminals of said mixer are each supplied with a plurality of 16'' tone signals falling within a predetermined compass collectively.
 15. A system according to claim 4 further including amplitude varying means coupled to said fifth tone coloring filter means for progressively reducing the amplitudes of a plurality of 4'' tone signals and those of a plurality of 8'' tone signals delivered from said keyer in response to operation of a plurality of keys on said keyboard means as their frequencies increase.
 16. A system according to claim 4 further comprising a first amplitude varying means connected between said keyer means and said fourth tone coloring filter means and a second amplitude varying means connected between said keyer means and said fifth tone coloring filter means; said first and second amplitude varying means each having a plurality of input terminals, a first and a second output terminal, a plurality of first resistors successively connected at one end to the plural input terminals respectively, and a plurality of second serially connected resistors of equal resistivity successively interconnecting the opposite ends of said plural first resistors with at least one second resistor coupled between successive opposite ends of said first resistors; said first and second output terminals being connected to the end terminals of the serial circuit comprised of said serially connected second resistors; said plural input terminals of each of said first and second amplitude varying means being so connected to said keyer means as to receive a group of 4'' tone signals and that of 8'' tone signals respectively whose frequencies progressively decrease from the input terminal which is coupled to the first resistor which is connected at its said other end to said first output terminal toward the input terminal which is coupled to the first resistor which is connected at its said other end to said second output terminal; said first and second output terminals of said first and second amplitude varying means being connected to said fourth tone coloring filter; and said second output terminal of each of said first and second amplitude varying means being connected to said fifth tone coloring filter.
 17. A piano tone-synthesizing system for electronic musical instruments comprising: keyboard means having a plurality of keys for initiating tone generation; a plurality of tone generators; keyer means for coupling out tone signals of 4'', 8'' and 16'' from said tone generators in response to operation of at least one key of said keyboard means; means coupled to the output of said keyer means for forming a first musical tone signal, said means including a tone coloring filter means for supplying the 4'' tone signals with the color of flute tone and means coupled to said tone coloring filter means for varying the levels of the 4'' tone signals as a function of their frequencies over a given range of frequencies; means coupled to the output of said keyer means for forming a second musical tone signal, said means including a tone coloring filter means for supplying the 8'' tone signals with the color of flute tones; means coupled to the output of said keyer means for forming a third musical tone signal, said means incluidng a tone coloring filter means for imparting the color of flute tones to the 16'' tone signals and means coupled to said tone coloring filter for varying the levels of the 16'' tone signals as a function of their frequencies over a given range of frequencies; means coupled to the output of said keyer means for forming a fourth musical tone signal, said means including a tone coloring filter means for supplying the 4'' and 8'' tone signals with the color of brass tones; means coupled to the output of said Keyer means for forming a fifth musical tone signal, said means including a tone coloring filter means for supplying the 4'' and 8'' tone signals with the color of string tones and means coupled to said tone coloring filter means for varying the levels of the 4'' 8'' tone signals as a function of their frequencies over a given range of frequencies; and means for combining said first to fifth musical tone signals in a predetermined ratio to generate a synthesized tone signal.
 18. A system according to claim 17 wherein said predetermined ratio in which the respective musical tone signals are combined in substantially 1:1:0.2:0.16:0.14. 